For many years the quinquina-tree of Loxa, the C. officinalis of Linnæus, was the only species with which botanists were acquainted; and from 1640 to 1776 no other bark was met with in commerce than that which was exported from the Peruvian port of Payta, brought down from the forests in the neighbourhood of Loxa. The constant practice of improvidently felling the trees over so small an area for more than a century, without any cessation, inevitably led to their becoming very scarce, and threatened their eventual extinction. As early as 1735 Ulloa reported to the Spanish Government, that the habit of cutting down the trees in the forests of Loxa, and afterwards barking them, without taking the precaution of planting others in their places, would undoubtedly cause their complete extirpation. "Though the trees are numerous," he added, "yet they have an end;" and he suggested that the Corregidor of Loxa should be directed to appoint an overseer, whose duty it should be to examine the forests, and satisfy himself that a tree was planted in place of every one that was felled, on pain of a fine.[21] This wise rule was never enforced, and sixty years afterwards Humboldt reported that 25,000 trees were destroyed in one year.
The measures adopted by the Spanish Government towards the end of the last century, in sending botanical expeditions to explore the chinchona forests in other parts of their vast South American possessions, led to the discovery of additional valuable species, the introduction of their barks into commerce, and the reduction of the pressure on the Loxa forests, which were thus relieved from being the sole source whence Peruvian bark could be supplied to the world.
The region of chinchona-trees extends from 19° S. latitude, where Weddell found the C. Australis, to 10° N., following the almost semicircular curve of the cordillera of the Andes over 1740 miles of latitude. They flourish in a cool and equable temperature, on the slopes and in the valleys and ravines of the mountains, surrounded by the most majestic scenery, never descending below an elevation of 2500, and ascending as high as 9000 feet above the sea. Within these limits their usual companions are tree ferns, melastomaceæ, arborescent passion-flowers, and allied genera of chinchonaceous plants. Below them are the forests abounding in palms and bamboos, above their highest limits are a few lowly Alpine shrubs. But within this wide zone grow many species of chinchonæ, each within its own narrower belt as regards elevation above the sea, some yielding the inestimable bark, and others commercially worthless. And the species of chinchonæ, in their native forests, are not only divided from each other by zones as regards height above the sea, but also by parallels of latitude. In Bolivia and Caravaya, for instance, the valuable C. Calisaya abounds, but it is never found nearer the equator than 12° S. Between that parallel and 10° S. the forests are for the most part occupied by worthless species, while in Northern Peru the important grey barks of commerce are found. In each of these latitudinal regions the different species are again divided by belts of altitude. Yet this confinement within zones of latitude and altitude is not a constant rule; for several of the hardier and stronger species have a wider range; while the more sensitive, and these are usually the most precious kinds, are close prisoners within their allotted zones, and never pass more than a hundred yards beyond them. All the species are, of course, affected by local circumstances, which more or less modify the positions of their zones, as regards altitude.
Thus, to give a geographical summary of the chinchona region, beginning from the south, it commences in the Bolivian province of Cochabamba in 19° S., passes through the yungus of La Paz, Larecaja, Caupolican, and Munecas, into the Peruvian province of Caravaya; thence through the Peruvian forests, on the eastern slopes of the Andes, of Marcapata, Paucartambo, Santa Anna, Guanta, and Uchubamba, to Huanuco and Huamalies, where the grey bark is found. It then continues through Jaen, to the forests near Loxa and Cuenca, and on the western slopes of Chimborazo. It begins again in latitude 1° 51´ N. at Almaguer, passes through the province of Popayan, and along the slopes of the Andes of Quindiu, until it reaches its extreme northern limit on the wooded heights of Merida and Santa Martha.
Humboldt remarks that, beyond these limits, the Silla de Caraccas, and other mountains in the province of Cumana, possess a suitable altitude and climate for the growth of chinchona-trees, as well as some parts of Mexico, yet that they have never been found either in Cumana or Mexico; and he suggests that this may be accounted for by the breaks which take place in Venezuela on the one hand, and on the isthmus of Panama on the other, where tracts of country of low elevation intervene between the lofty mountains of Cumana and Mexico and the chinchona region of the main Andes. In these low districts the chinchona-trees may have encountered obstacles which prevented their propagation to the northward: otherwise we might expect to find them in the beautiful Mexican woods of Jalapa, whither the soil and climate, and their usual companions the tree ferns and melastomaceæ, would seem to invite them.[22]
Be this how it may, the chinchona-plant has never been found in any part of the world beyond the limits already described.
The chinchonas, when in good soil and under other favourable circumstances, become large forest trees; on higher elevations, and when crowded, and growing in rocky ground, they frequently run up to great heights without a branch; and at the upper limit of their zone they become mere shrubs. The leaves are of a great variety of shapes and sizes, but, in most of the finest species, they are lanceolate, with a shining surface of bright green, traversed by crimson veins, and petioles of the same colour. The flowers are very small, but hang in clustering panicles, like lilacs, generally of a deep roseate colour, paler near the stalk, dark crimson within the tube, with white curly hairs bordering the laciniæ of the corolla. The flowers of C. micrantha are entirely white. They send forth a delicious fragrance which scents the air in their vicinity.
The earliest botanists gave the name of Chinchona to a vast number of allied genera, which have since been separated, and grouped under other names.[23] There are three characteristics by which a true chinchona may invariably be known; the presence of curly hairs bordering the laciniæ of the corolla, the peculiar mode of dehiscence of the capsule from below upwards, and the little pits at the axils of the veins on the under sides of the leaves. These characters distinguish the chinchona from many trees which grow with it, and which might at first sight be taken for the same genus. The fact, established by the investigations of chemists, that none of these allied genera contain any of the medicinal alkaloids, has confirmed the propriety of their expulsion from the chinchona genus by botanists; and Dr. Weddell gives a list of seventy-three plants, once received as Chinchonæ, which are now more properly classed under allied genera, such as Cosmibuena, Cascarilla, Exostemma, Remijia, Ladenbergia, Lasionema, &c.[24]
Thus thinned out and reduced in numbers, the list of species of Chinchonæ has been established by Dr. Weddell at nineteen, and two doubtful;[25] but even the classification of this eminent authority, published in 1849, already requires much alteration and revision. For instance: Dr. Weddell gives no place to the "red-bark" species, the richest in alkaloids, and one of the most important, which, through the recent investigations of Mr. Spruce, will now probably be admitted by botanists as a distinct species, the C. succirubra (Pavon). A new grey bark now introduced into India as C. Peruviana (Howard), and the C. Pahudiana (Howard), a worthless kind, cultivated by the Dutch in Java, will also be received as additional species. It seems likely also that the C. Condaminea requires to be divided into two or three distinct species; while the C. Boliviana (Weddell) will sink into a mere variety of the C. Calisaya.
The commercially valuable species, however, comprise but a small proportion of the whole; and, as all these have now been introduced into India, they alone deserve our attention. They are as follows:—